Final answer:
An unconscious patient can receive invasive medical treatment without a signed consent form under the principle of implied consent, whereas informed consent is usually required for adults, minors with parental consent, and elderly patients. A DNR can also dictate treatment in accordance with the patient's wishes.
Step-by-step explanation:
The individual who can receive invasive medical treatment without a signed consent form is an unconscious patient. In emergency situations where a patient is unable to give consent due to their condition (such as being unconscious), medical professionals have the legal and ethical obligation to provide lifesaving care without explicit consent. This is permitted under the doctrine of implied consent, which assumes that the patient would consent to treatment if they were able to do so. However, if a patient has previously made known their wishes through an advanced directive like a DNR (Do Not Resuscitate) order, these instructions should be followed. Informed consent is a fundamental principle in medical ethics and law, safeguarding patient autonomy by ensuring that they are fully informed about the risks and benefits of a treatment before agreeing to it. In the case of minors, consent must typically be obtained from a parent or guardian, whereas adults are generally expected to provide their own consent unless incapable of doing so.